Um .. Honestly, i wouldn't because first off out of all the females in the world why your best friend and if he had any respect for you, he wouldn't of cheated on you with her or anyone else. By the way, i don't think she's your best friend, she's not a friend at all.
You should take great caution not to go into it without agreeing on how the relationship will work out. The likelihood that he will repeat what he did before is very high. However, if you feel greatly convinced that you would love to give him a chance, you can go ahead.